These instructions are specific to the Virgin Mobile Samsung Galaxy S2 (SPH-D710BST).
If you do not have the Virgin Samsung Galaxy S2 please DO NOT follow this method for gaining Root access as it will most likely brick your phone!

This method uses an Odin One-Click Kernel for the Sprint Galaxy S2 to install a kernel that includes a Custom Recovery. Once booted into the Custom Recovery you can then flash Superuser which will root your phone and give you Superuser access. All Sprint kernels are compatible with the Virgin S2 and vice versa but it has been noted that the Virgin kernels are the recommended daily kernel.

Prerequisites

A PC running Windows with the Samsung Mobile Drivers Installed. The Samsung Mobile Drivers are available here.

Superuser (or SuperSU, MIUI Security, and etc) in a flashable zip, saved on your Internal or External SD Card. For this method I used SuperSU v1.25 (but any SU in a flashable ZIP should work). You can download several different versions here.

Although not required it is recommended that you have Samsung Kies installed on your PC as well. You can download Samsung Kies here.

Side-Effects

This method will trigger the Yellow Triangle upon start-up and will increase your Odin count.

It will also change your startup screen to look like the International GS2 startup screen. This is normal and can be fixed by flashing a stock kernel or running Triangle Away.
For instructions to clear the Odin count and remove the yellow triangle please go here.
If you would like to flash back to a stock Virgin S2 Kernel you can find them here.

Instructions

Open the One-Click.EXE kernel on your PC.
Once the One-Click.EXE file is opened you will be presented with a window that has a black title bar across the top, several empty boxes and a Start button.
Leave the screen up but do nothing else here for now.

Reboot your phone into Download/Odin Mode by holding down the Power and Volume Down buttons.

When prompted press the Volume Up key to continue.

Plug your USB cord into your phone and then plug the other end of the cord into an available USB slot.

Once the phone is plugged in you should see one of the white boxes on the One-Click.Exe program turn yellow.

Press Start on the One-Click.exe program.
If the flash is successful your phone will now reboot. This will take slightly longer than usual, this is normal. Depending on the kernel you are flashing there may or may not be a boot animation, please be patient while your phone reboots.

After the phone has completely rebooted power off.

Hold down Power and Volume Up to boot into Recovery.

Scroll down to "wipe cache partition" and press power.

Scroll down to "Yes - Wipe Cache" and press power.

Scroll down to "advanced" and press power.

Scroll down to "Wipe Dalvik Cache" and press power.

Scroll down to "Yes - Wipe Dalvik Cache" and press power.

Scroll down to "+++++Go Back+++++" and press power.

Select either "choose zip from sdcard" or "choose zip from internal sdcard" (depending on where you've saved the SuperSU.zip).

Navigate to where the SuperSU ZIP is saved and select it.

Scroll down to "Yes - Install .zip" and press power.

Scroll down to "+++++Go Back+++++" and press power.

Verify "reboot system now" is highlighted and press power.

Congratulations after your phone has finished rebooting you will be rooted! Enjoy!

If you have additional questions or would like to discuss these methods further please visit the Rwilco12 Android Forums.